Field of the Invention
The invention relates to a device and a method for calorimetrically measuring sorption processes.
Description of Related Art
For the energetic characterization of adsorbents on a gas-solid boundary surface, it is helpful to know the integral or respectively differential sorption enthalpies of the used gas-solid systems in addition to the sorption isotherms. In particular in the case of technical sorption processes, which occur in a non-isothermal manner in the gas phase almost without exception, this knowledge of the sorption heats is valuable since technical adsorbers represent quasi-adiabatic systems due to the relatively small surface-to-volume ratio.
Calorimeters can be based mainly on two different measurement processes. On the one hand, they can work according to the compensation principle, in which the heat tone to be measured is compensated for by an active heating or respectively cooling and the power necessary for this is detected. On the other hand, it can be based on the exchange principle, in which the heat flow generated by the heat tone leads to a temperature change between the sample and the surrounding area, which is detected.
Until now, on the one hand, microcalorimeters, which are typically equipped with a single sample cell, and secondly, dynamic difference calorimeters (DSC), which are operated with a sample cell and a reference cell arranged in a parallel manner, are available commercially. For technical and economic reasons, both types of calorimeters cannot be used for the simultaneous measurement of sorption isotherms and sorption enthalpy.
Technical literature contains isolated references to sorption calorimeters of scientific working groups, which almost exclusively concern apparatuses for laboratory experiments for university research that were developed and built internally by colleges/universities themselves. In general, we can differentiate between apparatuses for basic research, e.g. for examining bond enthalpies in the case of notably low surface assignment in a high vacuum, and apparatuses for the measurement of sorption and sorption enthalpy in procedurally relevant pressure and temperature ranges. The structure of the latter apparatuses is highly experimental, notably complex and thus very expensive. The conducting of measurements with these apparatuses is mainly manual due to the structure and functional principle of these apparatuses, is very involved and accordingly labor-intensive.
One of the biggest weaknesses of the currently existing apparatuses for the measurement of sorption and sorption enthalpy in procedurally relevant pressure and temperature ranges is that, in measuring mode, changes from external factors, device-specific changes as well as heat effects, caused by the change in the atmosphere in the measurement cells, cannot be taken into consideration. These heat effects can be, among other things, the heat input through a temperature of the supplied gaseous substance that is potentially different than the measurement cell or the heat received or respectively emitted during the expansion or respectively compression of the gaseous substance in the measurement cell. The evaluation of the data received with these measuring devices is also based on simplified models and different exceptions must be made for changes in the atmosphere inside the measurement cells, which leads to strong restrictions with respect to the accuracy of the obtained results.
Furthermore, these measuring devices lack the possibility of a reliable, fast and generally valid calibration, since, up until now, only a manual calibration has been possible, wherein a calibration must be performed before each individual measurement. This calibration is involved and reproducible values can only be obtained using these measuring devices with great effort, which are even then considerably less exact when compared with conventional calorimetry measurements and have many errors.